FA5527 FUJI [Fuji Electric], FA5527 Datasheet - Page 17

• Manufacturer Part Number: FA5527
• Description: Fuji Switching Power Control IC
• Manufacturer: FUJI [Fuji Electric]

(4) Blanking
increasing the threshold voltage based on CS pin
voltage.
based on FB pin voltage to keep power supply output
voltage constant.
520mV limits MOSFET over-current when FB pin voltage
is very high like 4V by overload etc.
maximum duty cycle of an OUT pulse and the maximum
duty cycle is set at 80% (typ.) using this pulse..
due to discharge current from the capacitor in the main
circuit or gate drive current. If the surge current reaches
the IS pin threshold voltage, current comparator output
could be inverted and normal pulses would not be
generated from the OUT pin.
the current comparator. When a trigger signal is input
from the oscillator, the blanking circuit outputs a
certain-width pulse signal as a PWM latch (F.F.) set
signal.
latch input signals, the output of PWM latch (F.F.) will not
be inverted while the set signal is input from the blanking
circuit, even if a rest signal is input from the current
comparator (IS comp.).
blanking time (200ns for FA5526/36, 400ns for
FA5527/37 and 600ns for FA5528/38) immediately after
an output pulse has been generated from the OUT pin
and does not respond to a surge current at turn-on.
（See Fig.8.）
a noise filter at the IS pin.
AN-087E Rev.1.0
April-2011
At start-up, soft start can be realized through gradually
At steady operation, the threshold voltage is varied
In addition, the maximum IS pin threshold voltage as
The oscillator generates a pulse to determine the
For details, refer to “9-(14) Timing chart”.
When MOSFET turns on, a surge current is generated
To avoid this, a blanking function is incorporated into
Since the set signal is given a high priority in PWM
As a result, the IS pin input voltage is ignored for a
In general, the blanking circuit eliminates the need for
Fuji Electric Co., Ltd.
FA5526/5527/5528/5536/5537/5538
FB
17
2
60k
20k
5V
Fig.7 Current comparator
3R
R
Cs
Fig.8 Blanking
http://www.fujielectric.co.jp/products/semiconductor/
Buf
x1
0.52V
1
3
CS
IS
11µA
IS comp.
VCC
Rs